A. Field of the Invention
The invention relates generally to paper cutting devices and particularly to paper web perforating devices having rotatable anvils against which multiple perforating knives mounted in spaced distances on the surface of rotating cylinders operate.
B. Description of the Prior Art
Machines and devices for perforating paper webs in the longitudinal and in the transverse direction are known in the art. Such devices have discs with perforating tools operating against die rings correspondingly having female discs and having further one or two cross perforating cylinders carrying one or more axially extending perforating knife blades arranged in slots in the surface of the cylinders, which operate against an anvil cylinder having a smooth, hardened surface. The perforating blades are adjusted in their slots in the perforating cylinders in such manner, that their cutting knife edges touch the hardened, smooth surface of the anvil cylinder without breaking or bending the cutting knife edges, thus cutting cleanly through the paper webs, which are fed over the anvil cylinder.
However it has become known that machines of this kind could only be operated at relatively slow speed when more than 2 perforating blades had been set 180.degree. C apart from another in the perforating cylinder. The problem was that difficulties started mounting with increased speed of the machine or when 4, 6 or 8 blades had been arranged at spaced circumferential distances on the periphery of the perforating cylinder. These difficulties resulted from vibrations of the anvil cylinder under the rythmic impacts of the perforating blades which inexplicably got bent and blunted knife edges from the periodical hammering at the hardened surface of the anvil, thus rendering a perforation impossible after a short operation, particularly in the center portion of the paper webs. By making the journal ends of the otherwise solid anvil cylinder stronger and/or by increasing and prestressing the cylinder bearings the adverse condition did not improve and that problem is now solved by the applicant's invention. The word "webs" should be understood to include the singular "web" as well as the plural.
The most relevant prior art are U.S. Pat. Nos. 1,018,155, 1,098,060, 1,714,583 issued to Bengoush, Spiller and Anthony respectively. None of these show an anvil cylinder or a knife blade cylinder like that taught in this application.